Method for the manufacture of heating cartridges



- April .1947- w. A. CALDWELL EI'AL 2,413,333

METHOD FOR THE MANUFACTURE OF HEATING CARTRIDGES Filed April 10', 1944Patented Apr- 1. 1941 2,418,333

METHOD FOR THE MANUFACTURE OF HEATING CARTRIDGES Walter AndersonCaldwell, West Kilbride, and Donald George Ashcroft, Saltcoats,Scotland, assignors to Imperial Chemical Industries Limited, acorporation of Great Britain Application April 10, 1944, Serial No.530,410 In Great Britain March 15, 1943 Claims. 1

The present invention relates to the manufacture of chemical heatingcartridges of the kind adapted for use in chemical immersion heaters andproduced by compressing, into the open end of a tubular envelope of adeformable material, a, chemical heating composition comprisinginorganic oxidising and reducing agents and adapted when ignited toreact with evolution of heat and formation of non-volatile reactionproducts without any considerable quantity of gaseous products.

For the purpose of igniting chemical heating cartridges of the kinddescribed there is employed at the open end of the envelope a moreeasily ignitable composition, of which the main reaction product islikewise a hot non-volatile residue. This may take the form of anigniter external to the compressed heating composition, but morefrequently the more readily ignitable composition is pressed over themain body of the chemical heating composition to form a prim- .ingcomposition and is in turn ignited by means of an igniter comprising astill more easily ignitable composition yielding a hot non-volatileresidue and located in external contact with the surface of the primingcomposition. This igniter conveniently comprises the said still moreeasily ignitable composition in a cemented form, and may be formedaround the end of a fuze.

The cartridge, whereof the envelope may consist of an insulatingmaterial such as asbestos paper, is intended to be slipped into a tubeof greater length than itself, so that the envelope at the end remotefrom the ignition end is incontact with the end wall of the immersionheater, while there is a space between the ignition end of the column ofthe charge and the venting end of the tube. Although in the immersionheater this space accommodates a filter and the necessary means forconducting the ignition from the primary source of ignition to theaforesaid compositions, it is to a large extent unoccupied by solidmaterial. The ignition end of the charge is 7 thus left in the immersionheater without any external support effective to prevent particles fromit becoming dislodged and scattered in transport and handling should thecompressed material tend to be lackingin cohesion, with the result thatthe contact between the lgniter and the end or the charge, or evenbetween the terminal priming portion and the main portion of the chargemay be impaired or broken; and the main portion of the char e may thusfail to be ignited. The compositions ordinarily used for the charge arebased on mixtures of metallic oxides and reducing elements or compounds,and these usually have poor binding properties.

In the process hitherto employed for the production of the heatingcartridges, the envelope of deformable material is inserted into amoulding cavity defined by a channel in a block of rigid material and anend wall, also of rigid material capable of relative motion thereto, thecomposition or compositions is or are introduced an: eventually theplunger is advanced until thr charge has been compacted to the requiredex tent, and is then retracted, whereupon a termi nal aperture is openedby relative motion be tween the block and the end wall, and the cartridge is expelled by advancing a plunger. I! practice very considerablepressures are requirel to produce serviceable cartridges; and as thplunger is retracted from the charge in the mould ing cavity, owing tothe resilience of the mass 0 particles pressed against the envelopelining th rigid wall of the mould cavity, an expansiv movement ofrecovery of the particles tends t take place towards the ignition end ofthe charg with the result that the surface at this end is nosatisfactorily consolidated. The cross section: area of the expelledcartridge is also greater tha that of the moulding cavity.

The plunger employed has usually a protubei ance on its working end inorder to recess the en surface of the compacted composition for the pu1pose of increasing the area of contact, betwee the charge and theexternal igniter, and whe the plunger is so shaped its withdrawal permiexpansive movement of the particles in a directic inwards from the rigidwall of the channel tr wards the recess, which increasesthe tendem toloose packing of the composition or compos tions at the ignition end ofthe cartridge, at Whl( end it is most important that the packing shou befirm in order to ensure certainty of action the cartridge ashereinbefore explained.

The principal object of the present inventi is to provide, in themanufacture of chemic heating cartridges of the kind described, a m orimproved method of compressing the heatil composition or compositionsinto the envelope. A further object of the present invention is toprovide an improved process for the manufacture of heating cartridges ofthe kind described in order to reduce the occasional risk that, onactuation of the ignition means, the cartridge may fail to act.

According to the present invention a method for the manufacture ofchemical heating cartridges of the kind described comprises loading aheating composition into an open ended tubular envelope of deformablematerial, advancing a press plunger in order to compact the heatingcomposition within the envelope while the same is supported in a presschamber, thereafter maintaining the press plunger in contact with thecomposition, causing relative displacement between the end closure ofthe press chamber and said press chamber while so maintaining the pressplunger in order to leave an aperture through which the cartridge can beexpelled, and expelling the cartridge by advancing the press plunger.Preferably the press plunger, after compacting the heating composition,is maintained in contact therewith under a pressure which isinsufllcient to expel the cartridge through the aperture when the endclosure is displaced, the pressure on the press plunger being thereafterincreased in order so to expel the cartridge.

Figure 1 is a vertical section of a heating carbridge made in accordancewith the method of the present invention.

Figure 2 is a vertical sectional view of an-apparatus which may be usedto carry out the method.

Figure 3 is a similar, fragmentary view of a mbsequent step in themethod and,

Figure 4 is a view like Figure 3, showing another step.

The process of the present invention may be :arried out in a presshaving a press chamber of tubular form and provided with a press ilungerH actuated, for example by means of t screw or hydraulic mechanism l2,the press :hamber being provided with a sliding or other 1nd closure I5adapted for easy and rapid disilacement, under the influence of anydesired tctuating mechanism, as indicated at 15' in igure 2. If desiredautomatic means may be mployed to control the sequence of compressing heheating composition, reducing the pressure, I

pening the end closure I5, and increasing the -ressure to expel thecartridge.

When the cartridge 20 is formed according to he method of the presentinvention, using a ompactingpressure not less than about 4 tons orsquare inch, the ignition end 2| is found to l e well consolidated, andfailures of the more asily ignited composition 22 forming the igniter 1contact with the end of the charge 23 to bring bout the reaction of thewhole cartridge when has itself been ignited are reduced in freuency.

The invention is further illustrated in the foliwing example.

Example The moulding channel In in a pneumatic press as a diameter of.963 inch, and the press plunger I a diameter of .850 inch. The envelope25 )l'lSiStS of three thicknesses of asbestos paper 4 of an inch thick,wrapped into the form f a tube and turned over to form an end closure 5.The resulting asbestos tube, which weighs cont 6 grams, is introducedinto the cavity In l the moulding block l6 so as to rest on the end latel5, and there is first introduced into it a charge of about to 48 gramsof a mixture of the composition,

- Per cent Calcium silicide 4B Hammer-scale 46 China clay 8 This isshaken down by tapping the moulding block l6, and then a furtherchargeof 5 grams of a mixture of the composition, 4

is added and similarly shaken down. The plunger H is brought down on tothe surface of the last mentioned composition under a dead load of 2%tons,- and the material compressed, as shown in Figure 3. The pneumaticpressure is then relieved to such an extent that the dead load pressureon the charge of the cartridge is about one hundredweight, and the endwall l5 of the cavity In is moved away so as to uncover its end. Thedead load on .the plunger II is thereupon increased until the cartridge20 is bodily ejected, as indicated in Figure 4, which usuallynecessitates a dead load not less than about five hundredweights. Theend face of the press plunger II has a paraboloid projection l'|- whichextends for about I; of an inch at its maximum height, which is at thecentre of the face, so that the surface 2| of the last mentionedcomposition in the cartridge is correspondingly dimpled, as indicated at28. This cartridge proper.

The cartridge 20, which after expulsion has a diameter slightly greaterthan the diameter of the moulding cavity I I], is slipped intoa metaltube 30 in which it forms a sliding fit.

The asbestos paper envelope 25 of the cartridge extends beyond theignition end 2| of the charge sufficiently to provide a thermalinsulation between the whole column of the hot residue obtained as aresult of the reaction and the wall of the tube 30, which extendsslightly beyond the end of the envelope of the cartridge.

A metal framework spacer 3| is inserted so as to rest on the surface 2|of the compressed composition at the ignition end of the charge, andthere is also inserted a quickmatch fuse 32 terminating in a bead 33weighing about 0.2 gram of a mixture of red lead 69 per cent., calciumsilicide 29 per cent. nitrocellulose of high viscosity characteristics 2per cent. made by evaporation from a dope consisting of a suspension ofthe mixture of red lead and calcium silicide in a nitrocellulosesolution, so that the bead is accommodated in juxtaposition to thecompressed priming composition 22 in the dimple 28 formed in the latter.The spacer 3| extends about the same distance as the end of the envelope, and on top of it is pressed a pad 34 of asbestos wool whichforms a gas filter. The chemical immersion heater is then provided witha terminal wall 35 having a vent 36 through which the end of the fuse 32is accessible, and this vent is provided with a suitable temporaryclosure such as a tear-oil 31. Such a chemical immersion heater may beembodied in a selfheated food or beverage can.

We claim:

1. The method of making a chemical heating cartridge, which comprisessupporting one end and the side walls of a tubular envelope ofdeformable material against deformation, substantially filling theenvelope with a pulverant heatcompletes the" ing composition, applyingendwise compacting pressure to the composition from the open end of theenvelope, decreasing but not completely relieving the pressure, removingthe end support for the envelope, and then increasing the compactingpressure to discharge the envelope and the compacted composition fromthe side wall s pport.

2. The method of making a chemical heating cartridge, which comprisessupporting the end and side walls of a tubular envelope of deformablematerial against deformation, substantially filling the envelope with apulverant heating composition, applying endwise compacting pressure tothe composition from the open end of the envelope, without completelyrelieving the pressure, decreasing the same to an amount insufiicient tomove the envelope bodily when the end support is removed, removing theend support, and then increasing the compacting pressure to dischargetheenvelope and the compacted composition from the side wall support.

3. The method of making a chemical heating cartridge, which comprisessupporting the end and side walls of a tubular envelope of deformablematerial against deformation, substantially filling the envelope with apulverant heating composition, applying endwise compacting pressure tothe composition from the open end of the envelope, and simultaneouslymoulding a cavity in the end face of the composition, decreasing, butnot completely relieving, the pressure, thereby preventing expansion ofthe composition adjacent the open end of the envelope, removing the endsupport for the envelope while the pressure is so decreased, and thenincreasing the compacting pressure to discharge the cartridge from theside wall support.

4. The method of making a chemical, heating cartridge, which comprisessupporting the end and side walls of a tubular envelope of deformablematerial against deformation, substantially filling the envelope with apulverant heating composition, applying endwise compacting pressure tothe composition from the open end of the envelope, reducing, but notcompletely relieving, the pressure at the open end of the envelope,thereby preventing expansion of the compacted composition at the end,relieving the support at the opposite end of the envelope while thepressure is reduced, and thereafter applying additional pressure to theopen end to discharge the cartridge from the side wall support.

5. The method of making a chemical heating cartridge, which comprisespositioning a tubular envelope of deformable material having a closedend in a mould cavity of corresponding shape, substantially filling theenvelope with a pulverant heating composition, applying endwisecompacting pressure to the composition from the open end of theenvelope, thereafter decreasing, but not completely relieving, thepressure, thereby holding the composition at the open end of theenvelope against expansion resulting from the release of pressure,opening the closed end of the mould cavity to permit expansion of thecartridge in that direction, and increasing said pressure to dischargethe cartridge through the last mentioned end of the cavity.

WALTER ANDERSON CALDWELL. DONALD GEORGE ASHCROFT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,200,577 Lozon May 14, 19402,121,635 Krapp June 21, 1938 2,357,863 Young et al. Sept. 12, 1944

